Nickel oxide interlayers for photoconductive elements

ABSTRACT

A process for applying a photoconductive layer to a flexible nickel or nickel-coated substrate by initially subjecting a nickel sheet or belt to an acid etching bath followed by anodizing treatment in an electrolytic bath to obtain at least two intermediate metal oxide layers such as nickel oxide layers having superior adhesive and charge-injection-blocking characteristics; and a flexible photoreceptor element with such structure which is especially useful for high-speed xerographic copy work.

United States Patent Pinsler Oct. 21, 1975 [54] NICKEL OXIDE INTERLAYERSFOR 3,511,661 5/1970 Rauner et al. 96/86 PHOTOCONDUCTIVE ELEMENTS3,684,572 8/1972 Taylor [17/213 Inventor: Heinz W. Pinsler, Brighton,N.Y.

Xerox Corporation, Stamford, Conn. j

Filed: Feb. 8, 1974 Appl. No.: 440,907

Related US. Application Data Division of Ser. No. 332,044, Feb. 12,1973.

Assignee:

References Cited UNITED STATES PATENTS 12/1946 Peters ..117/200 2/1949Stockdale 117/230 Primary ExaminerRoland E. Martin, Jr.

Assistant ExaminerJ. L. Goodrow Attorney, Agent, 0r FirmJohn E. Crowe;James J. Ralabate; James P. OSullivan [57] ABSTRACT A process forapplying a photoconductive layer to a flexible nickel or nickel-coatedsubstrate by initially subjecting a nickel sheet or belt to an acidetching bath followed by anodizing treatment in an electrolytic bath toobtain at least two intermediate metal oxide layers such as nickel oxidelayers having superior adhesive and charge-injection-blockingcharacteristics; and a flexible photoreceptor element with suchstructure which is especially useful for high-speed Xerographic copywork.

6 Claims, N0 Drawings NECKEL UXTDIE TNTlERLAt ERS FQR PHQTUCGNDUCTTVEELEMENTS This is a division of application Ser. No. 332,044, filed Feb.12, 1973.

This invention relates to fast, highly flexible photoreceptor elementsand to a process for obtaining such elements comprising a nickel ornickel-coated substrate, particularly of the belt type, having aphotoconductive layer strongly affixed thereto and joined in goodblocking and charge injection-preventing contact with the substratethrough the utilization of at least two intermediate nickel oxideblocking layers arranged between the substrate and the photoconductivelayer.

In the xerographic art, a photoconducting insulating layer is firstgiven a uniform electrostatic charge in order to sensitize its surface.The layer is then exposed to an image as defined by electromagneticradiation, such as light, which selectively dissipates the appliedcharge in the illuminated areas of the photoconducting insulating layerwhile leaving behind a latent electrostatic image in the non-illuminatedareas. The latent electrostatic image may be developed and made visibleby deposited finely divided electroscopic marking particles on thesurface of the photoconductive layer. This concept was originallydescribed by Carlson in U.S. Pat. No. 2,297,691 and is further amplifiedand described by many related patents in the field.

Conventionally, a xerographic photoreceptor plate includes a supportingconductive base or substrate which is generally characterized by theability to accommodate the release of electric charge upon exposure ofthe photoconductive member to activating radiation such as light.Usually, this substrate must have a specific resistivity of less thanabout 10" ohm-cm, preferably less than about 10 ohm-cm and havesufficient structural strength to provide mechanical support for aphotoconductive member.

The conventional xerographic plate also normally has a photoconductiveinsulating layer overlaying the conductive base or substrate.Photoconductive layers may comprise a number of materials known in theart. For example, selenium-containing photoconductive material such asvitreous selenium, or selenium modified with varying amounts of arsenicare found suitable. In general, however, such photoconductive layer musthave a specific resistivity greater than about ohmcm in the absence ofillumination and preferably at least 10 ohm-cm. in addition, theresistivity should drop at least several orders of magnitude in thepresence of activating radiation or light. This layer should alsosupport an electrical potential of at least about 100 volts in theabsence of radiation and customarily may vary in thickness from about 10to 200 microns.

A photoconductive layer having the above configuration, normally willexhibit some reduction in potential or voltage leak even in the absenceof activating radiation. This phenomenon is known as dark decay and willvary somewhat with usage of a photoreceptor. The existence of theproblem of dark decay is well known and has been controlled to someextent by incorporation of thin barrier layers such as a dielectricmaterial between the base or substrate and the photoconductiveinsulating layer. U.S. Pat. No. 2,901,348 to Dessauere't al utiiizes afilm of aluminum oxide (Ex. 25 to 200 angstroms) or an insulating resinlayer, such as polystyrene (Ex. 0.1 to 2 microns) for this purpose. Withsome limirations, such barrier layers function to allow thephotoconductive layer to support a charge of high field strength whileminimizing charge dissipation in the absence of illumination. Whenactivated by illumination, however, the photoconductive layer shouldstill become conductive and permit a migration of the existing chargesthrough the photoconductive layer in the radiation orillumination-struck areas.

In addition to the electrical requirements of a barrier layer, it isnecessary that all photoreceptor layers also meet certain requirementswith regard to mechanical and chemical properties.

These requirements become particularly important when one attempts toutilize xerographic processes in modern automatic copiers operating athigh speeds. For such purpose it has been found very useful to utilizephotoreceptors in the form of endless belts (ref. U.S. Pat. No.3,691,450).

While belt-type photoreceptors have the advantage of greater speed forxerographic copying purposes, there are also serious technical problemsinherent in their use. For example, high speed machine-cyclingconditions demand strong adhesion between a photoconductive layer andthe underlying substrate compared with the slower aluminum photoreceptordrum which does not substantially flex.

It is also very important that any interface between the electricallyconductive supporting substrate and the photoconductive layer bechemically stable since changes at this point will have a substantialeffect on the electrical properties of the photoreceptor.

In searching for suitable photoreceptor materials it has been found thatnickel or nickel-coated substrates are useful. Seamless belts of thismaterial have satifactory mechanical and chemical properties and can bereadily produced by techniques known to the art.

Unfortunately, however, belts of this material also have somelimitations or deficiencies. For example, it is difficult to findsuitable blocking layers for controlling charge-injection" while stillavoiding a flaking off or spalling of the photoconductive layer.

The concept of charge-injection is known and recognized, in thatelectrical currents far in excess of ohmic currents can provably bedrawn through insulators from the electrodes, (ref. Physical Review 97No. 6, 1538, 1955; Rose, Concepts In Photoconductivity and AlliedProblems, Interscience Publishers, John Wylie and Sons, 1963). Thephenomenon is sometimes analogized to a vacuum diode in which thecathode thermally emits electrons into the vacuum and a space charge isbuilt up between the cathode and the anode. Where an insulator isinvolved, the carrier concentration exceeds the equilibriumconcentration whenever charge is injected from the electrodes. Theflowing electrical current, in such case, is space-charge-limited, andgreater than the normal ohmic current expected with equilibrium carrierconcentrations. The magnitude of such space-charge-limited current isdifficult to predict (in any case) because of the presence and effect oftraps on charge transport through a photoconductive material. Generallyspeaking, charge injection can and should be prevented or at leastlimited to insure chargeability of the photoconductor and by darkdischarge. Merethickness of insulating layer alone, however, will notprovide a suitable answer since an intolerable residual voltage can bebuilt up if an insulating layer becomes too thick.

It is possible to prevent or at least to limit charge injection throughthe careful choice of interface materials having a work function suchthat they form a blocking layer with the photoconductive layer. In thiscontext the ,term work function is defined as.

a difference in energy level between electrons present in a particularmaterial and those calculated at infinite distance in vacuo; i.e., abinding energy.

Within the above definition, an electron blocking contact is formed forxerographic purposes whenever the electronic work function of the metalsubstrate is larger than that of the overlying photoconductive insulatorlayer. If, on the other hand, the electronic work function of thesubstrate is smaller than the photocon' ductive insulator, electrons areinjected into the system.

In attempting to determine the efficiency of a particular interface fromthe relative work functions of the joining materials, it has been foundthat small amounts of adsorbed impurities on surfaces forming interfacematerials will also cause substantial changes in work function.Unfortunately, this can happen when amorphous selenium or seleniumalloys are utilized in a photoconductive layer. In fact, such materialcustomarily includes small amounts of chlorine and arsenic (ref.Xerography and Related Processes; J. H. Dessauer and H. E. Clark). Theinjection of electrons from an interface area will dark-discharge aphotoreceptor when the photoconductor surface is charged positively anda negative electric counter charge is induced at the substrate.

It is further noted that a material which conducts only holes can alsobe employed as an electron blocking interface, provided it is depositedas a thin layerbetween the photoconductive layer and thechargeconducting substrate. Such material includes, for instance,chlorineand arsenic-rich selenium.

It is an object of the present invention to obtain improved flexiblephotoreceptor elements for xerographic copying purposes, in which anickel or nickelcoated charge conductive substrate layer and aphotoconductive layer, particularly a selenium-containingphotoconductive layer are strongly bonded without loss ofcharge-injection-blocking properties.

I It is a further object of the present invention to obtainphotoconductive layers affixed to a nickel or nickelcoated substrate bychemically stable flex-proof bonding which is easily applied.

It is a still further object of the present invention to obtain, prepareand employ an efficient metal oxide blocking contact suitable for usewith a nickel-selenium alloy interface of a flexible belt-typephotoreceptor component.

These and other objects of the instant invention are accomplished bymicroetching a nickel or nickelcoated substrate such as metallized paperor metallized plastic belt with an etching composition comprising aninorganic acid, inclusive of phosphoric, sulfuric or hydrochloric acid,or combination thereof, in the presence of at least one of palladiumchloride, chloroplatinic acid or ferric sulfate. This step is followedby anodizing the resulting microetched chemically oxidized substrate,preferably by immersing the substrate as an anode in an electrolyticbath and/or by glow discharge such as described, for instance, byIgnatov in J. Chimie Physique, 54 (1957) pg. 96 et seq.

um-containing photoconductive layer of one of the usual type upon thetreated substrate to obtainthe desired photoreceptor element.

Preferably, nickel or nickel-covered substrate suit-' able for use inphotoreceptor elements within the present invention are kept free ofsurface. contaminants, other than necessary additives such as dopants.This pre-condition can be easily obtained through the use of one or morecleaning steps wherein the substrate is initially immersed for a briefperiod into a cleaning bath.

Suitable cleaners for suchpurpose are sold commer-' cially, and areexemplified, for instance, by Mitchell Bradford No. 14 Cleaner and byMobil .Acid Cleaner. The cleaned and well-rinsed substrate is optionally further treated with a pre-etch acid wash solution, preferablyone containing an inorganic acid solution such as hydrochloric acid orphosphoric acid, and. additionally containing 0% up to about a catalyticamount of at least one of palladium chloride or chloroplatinic acid. Forsuch purpose a catalytic amount is usefully defined as the concentrationof palladium chloride or chloroplatinic acid sufficient to substantiallyaccellerate a combined etching and chemical oxidation reaction at thesurface of the nickel substrate when the washed substrate issubsequently exposed to the required etching and oxidizing composition.Generally speaking, a satisfactory concentration of catalyst in l apre-etch acid wash solution (when used) varies from corresponding acidconcentration can usefully, although not exclusively, vary from about15% to 55% by weight.

When desired, the full catalytic amount of platinum or palladium can besupplied byinclusion of one or both in (a) the pre-etch acid washsolution, (b) in the etching composition, or (c) in both the washsolution and etching composition. In each case, however, a totalsolution concentration of about 0.01% 0.10% by weight is foundsufficient to assure an adequate catalytic deposition on the nickel beltsurface, provided proper temperature and time conditions are met. By wayof example, a pre-etch acid washing step is preferably carried out at atemperature range of about 15C C, for a period of about 1-5 minutes.

The microetching step, on the other hand, can be usefully carried out ata somewhat higher temperature range of about 20C l 10C and for a periodof about 2-15 minutes. Where increased concentrationand/or differencesin temperature are permitted, however, the treatment time can be variedsomewhat without substantially affecting the desired properties.

Generally speaking, a suitable etching solution for purposes of thepresent invention can comprise 1. an inorganic acid solution containingat least one: of phosphoric acid, sulfuric acid or hydrochloric acid;

2. a balance of 0% up to about a catalytic amount of at least one ofpalladium chloride or chloroplatinic acid based on the total amount ofcatalyst utilized in the .acid wash and micro etching steps, and

3. from up through about l0%'by weight of a water soluble alkali metalhalide or metal sulfate.

In addition to the optional inclusion of catalyst, the etching bath usedin the present invention can usefully include a water soluble alkalimetal halide or a metal sulfate salt exemplified by KCl and Fe (SO Aconcentration range of from 0% up through about 10% by weight of suchmetal salts is found useful, provided a minimum of about 8% 10% byweight of the metal sulfate such as Fe (SO,,) is utilized in the absenceof either platinum or palladium catalyst in the acid washing and etchingbaths.

The amount of inorganic acid or acids present in the etching compositioncan usefully vary, a concentration of about 10% 60% by weight beingsuitable, and a concentration of 10% 25% by weight being preferred forpurposes of the present invention. The presence of phosphoric acid inthis etching composition is a further preferred embodiment of thepresent invention.

Afte exposure to the etching composition, such as by dipping, the washedmicroetched and oxide-coated substrate is subject to an anodizing stepby immersing and treating as an anode in an electrolytic bath until thepotential of the electrode as measured against a saturated calomelelectrode changes from a negative value to a value not exceeding about0.85 volt. In this step a second oxide coat is applied over the previouschemi- Cally-applied metal oxide coat on the nickel substrate. For thepurpose of applying such additional coat it is convenient, for instance,to immerse the substrate (i.e., the belt) as an anode in an electrolyticbath with a chromate salt solution as electrolyte. This bath canusefully operate at an applied current of about 3-10m A/cm until theanode potential (with current cut off and measured against a saturatedcalomel electrode), has the maximum potential value indicated above.This step is most efficiently carried out at a current density of about-1OmA/cm and for a period ,varying from" about 1-15 minutes.

Suitable electrolytes for the electrolytic bath include, for instance, a5-15% solution (by weight) of Na Cr- O K Cr O Na- CrO K CrO or H CrO atroom temperature up to about 95C, and preferably about 50C through 95C.The parameters of (1) temperature (2) electrolyte concentration and (3)current density are inversely related to the anodizing treatment timefor purposes of obtaining a suitable second oxide layer on the belt.

In addition to, or as an alternative to, the abovedescribed step, it isalso found useful to lay down a nickel oxide layer by glow dischargetechnique. Here the nickel substrate is made the anode under partialvacuum, with a current density of about 3 X A/cm and a voltage (cathode)of about 2.5 K.V. for a period of about l-5 minutes. This technique ismodified and described in detail in V0]. 54 of J. Chimie Physique,(supra).

After washing, a photoconductive layer, preferably a selenium-containingphotoconductive layer, is deposited upon a surface of the treated andwashed substrate to complete the major components of the photoreceptorelement. For this purpose it is found convenient to utilizeselenium-containing photoconductor material and techniques as described,for instance, U.S. Pats. Nos. 2,753,278,'2,970,906, 3,312,548 and3,490,903;

a particularly suitable technique involves sealing sele- L nium, arsenicand a halogen in a container under .heat

to form ahomogenous material, which is then applied onto a cooledsubstrate by evaporation from a lined crucible under vacuum. Suitablephotoconductive layers applicable to the present invention include, forinstance, a cadmium selenide, a gallium triselenide, an arsenictriselenide, an antimony-selenium-or seleniumarsenic-halogen layer. Alsoincluded are photoconductive layers containing Tellurium, Germanium andBismuth.

The following examples specifically demonstrate preferred embodiments ofthe present invention without limiting it thereby;

I EXAMPLE'I A. A stain-free nickel alloy test beltidentified as A-l,having a thickness of about 4.5 mil (0.0045inch), a width of 5 inchesand a circumference of inches, is cleaned with an aqueous solutioncontaining 10% by weight of Mitchell Bradford No. 14 Cleaner, waterrinsed in deionized water for about 2 minutes, immersed in an acid washsolution (10% by volume 85.5% H PO for 1 minute, and then immersed for10 minutes at 60C in an etching bath containing l8g/liter KCl, 150ml/liter of 85.5% H PO and 0.2lg/liter of 10% chloroplatinic acid (HPrCl 6H 0) as a catalyst. The belt is then rinsed, dried and evaluated(Table I).

B. An identical nickel test belt identified as A-2 is treated as inprocedure A (supra) with the exception that the rinsing step indeionized water prior to microetching is extended to a full 5 minutes.

The results obtained in Steps A and B are examined microscopically andGloss measurements made in the usual way in accordance with thefollowing descriptions, and reported in Table I.

Microscopic Examination The morphology of the etched nickel foilis-examined by a scanning electron microscope and an optical microscope,applying ultramicrotome techniques to obtain vertical cross sections ofthe foils.

Gloss Measurements 4 Any change of the surface structure of the nickelbelt is noticeable by a change in reflectivity. The gloss value ismeasured with a Hunter Lab D16-75 gloss meter which measures therelative reflectance of treated and untreated surfaces using a incidentlight beam.

good microetched belt surface. Gloss 3% of reflectance The above resultssuggest considerable sensitivity to contamination when chloroplatinicacid is used as a catalyst.

EXAMPLE II A nickel test belt identical with the one used in Example I,and identified as A-3 is treated as in Example I A except that a PdClcatalyst is utilized by immersing the belt in a pre-etch acid washsolution containing 0. 25g/liter PdCl and 300 ml/liter of concentratedl-ICl. The micro etching step is then carried out for 5 minutes ina bathcontaining 650 ml/liter of85.5% H PO and 80 g/liter of KCl; withevolution of some chlorine byproduct. The microetched belt is thenrinsed and dried as in Example I and evaluated (Table 11) before furthertreatment.

EXAMPLE III A nickel test belt identical with those used in Examples HI,and identified as A-4, is immersed for minutes at about 76C in anagitated alkaline solution containing by weight of a commercial cleaner(Mitchell Bradford No. 14 Cleaner), rinsed for 2 minutes in deionizedwater then cleaned once more in a commercial cleaning solution (1/12strength Mobil Acid Cleaner), rinsed for 2 minutes in deionized water,dipped into an acid wash solution (300 ml/liter of concentrated I-ICl)for v30 seconds, dipped into an acid solution containing .25 g/literPdCl and 300 ml/liter of concentrated HCl for 10 seconds, then etched ina KC]- free etching bath containing 650 ml/liter of 85.5%'

H PO the microetched belt is then subject to the usual rinsing anddrying steps as in Examples 1-11 and evaluated (Table II) before furthertreatment.

EXAMPLE IV For nickel test belts identical with those used in Ex+ amplesI-IV, and identified as A5-8, are cleaned and rinsed in deionized wateras in Example I then immersed (without a preetch acid wash) in anetching solution containing 184 g/liter of Fe (SO.,) and 97.5 g/liter ofH 80, at 85C. After treating the four belts in the etching bath forvarying periods of time, they are removed, rinsed and dried as inExample I and evaluated (Table II), before further treatment.

EXAMPLE v1 (Control) A stain-free nickel test belt identical with thoseused in the preceeding examples, and identified as A40, is

cleaned and rinsed, then oxidized at 110C for 7 minutes in an etchingbath consisting essentially of 65.0 ml/liter of concentrated H POsolution. The oxidized nickel belt has a dull appearance and isevaluated as G (see Table II footnote).

EXAMPLE VII A. Samples from test belts A 1-9 of Examples I-IV are nexttreated for 10 minutes in an electrolytic bath containing sodiumchromate solution as electrolyte (10% by weight at pl-I6), operating at90C with a current density of 5 mA/cm After treatment, thetest belts arerinsed with deionized water, air dried, and

, then mounted onto a circular rotatablemandriland coated in a vacuumchamber (5 X 10* Torr) over a stainless steel crucible containing aheated selenium alloy consisting of about 99.67% selenium, 0.33%arsenicand about 30 parts per million chlorine at a temperature of about 280Cfor minutes. During this period the mandril is constantly at about 6revolutions per minute to obtain an external photoconductor sur- TableII (Step 1) Belt No. Cat. Pre-etch Etch Time Observation and GlossBath(s) Bath (min.) Test A-3 PdCl Yes, with H PO, 5 Ex.* etching andoxide Cat. KCl layer. Gloss=2% reflectance. Cl evolved A-4 PdCl Yes,w/Cat. H PO 5 Ex.* etching and oxide layer. Gloss=3% reflectance. No C1evolved.

A-5 NO H 80 2 G.* etching and oxide Fe (SO.), layer. Gloss=7reflectance.

A-6 2 Vg.* etching and oxide layer. Gloss=3% reflectance.

A-7 5 Ex. etching and oxide layer. Gloss=2% reflectance.

A-8 5 Vg. etching and oxide layer. Gloss=3% reflectance.

Ex. Excellent Vg'. Very Good g. Good EXAMPLE V rectly coated with aselenium photoconductive layer as A stain-free nickel test beltidentical with those used in the preceeding examples and identified asA-9 is cleaned and rinsed, then microetched at C for 10 minutes. Boththe acid wash and etching baths are iden-,

in Example VII without the prior 10 minute treatment in an electrolyticbath. This belt is then tested for mechanical and electrical propertiesas in Example VII A and the results reported in Table III. 1

For testing purposes the following guidelines and definitions aregenerally applicable in evaluating the results obtained:

Cold Test The flexible coated photoreceptor belt 1 I is mounted over two5-inch cardboard inserts and placed in a storage box and held at -28.8Cfor 4 hours.

' To pass the test, the photoconductive coating must remain intactwithout cracking or spalling.

Shock Test A photoreceptor belt, while still in a storage box, isdropped from a 42 inch height onto a supporting floor. To pass the testthe belt must remain intact and be substantially undamaged.

Flex Test Each belt is mounted on a tri-roller as- What is claimed is:

1. A photoreceptor element comprising a nickel or nickel-coatedsubstrate and a photoconductive layer joined in good blocking andcharge-injection preventsembly adapted to rotate the belt over eachroller at ing contact with the substrate through at least two inabout43C. The belt is cycled for 1000 cycles in 30 termediate nickel oxideblocking layers arranged bemmlltes- T test repeated (with 5 minute a s)for tween the substrate and the photoconductive layer, ob- 30,000 cyclesor until the belt structurally fails. To pass i d b h process comprisingthistest the belt must complete 30,000 cycles w tho microetching thenickel or nickel-coated substrate exhlbltmg cracks Whlch are Ylslble tothe with an etching composition comprising an inor- Mandrel T i beltbent three Over a ganic acid selected from the group consisting ofCylmder havmg a mch dlametef at Room p phosphoric acid, sulfuric acidand hydrochloric ture and then checked for cracks in the substrate andacid, in the presence of at least one of palladium layers PP 15chloride, chloroplatinic acid, or ferric sulfate;

Elctrlcal Dark Dlscharg? Test The Photoreceptor anodizing the resultingmicroetched chemically oxibelt is charged at 900 volt in the dark andthe potential dized Substrate. and gg aftler 3 seconds' i decay :1voltage a depositing a photoconductive layer upon the treated O 0 or e55accepta e or gener Xerograp 1c substrate to obtain the desiredphotoreceptor elepurposes. mem

Vc. Determination Test An electrical charge is added stepwise to aphotoreceptor surface in the dark 2. The photoreceptor element of claim1 wherein the and it is determined at what voltage the chargingbephotoconductive layer is a selenium-containing photohavior of thephotoreceptor begins to substantially deconductive layer. viate (by 40volts) from the desired (linear) charging characteristics. A maximumvoltage of 900 volts 950 3. A photoreceptor element comprising a nickelor volts is considered fair, 950 volts l 100 volts is good,nickel-covered substrate and a selenium-containing l 100 1500 volts isvery good and 1500 1600 volts photoconductive layer joined in goodblocking contact is considered excellent. through at least twointermediate blocking layers ar- Print Test About 50 square inches ofphotorecepranged between said substrate and the applied phototor aredark charged at 900 volts and developed withconductive layer, obtainedby the process out light exposure after about 20 seconds using fine a.microetching the nickel or nickel-coated substrate powdered toner. Thepresence of light or dark spots or with an etching compositioncomprising a visible pattern is attributed to uneven dark discharge 1.an inorganic acid solution containing at least one of the photoreceptorattributable to non-uniformities of phosphoric acid, sulfuric acid, orhydrochloric of the interface. acid,

Table III Belt Mandrel Cold & Shock Flex Electrical Vc Print (coated)Test Test (28.8C) Test Dark Dis- Test Test (1.25" charge Test Diam) 12%3 Sec.

A-l Passed Passed Failed Passed Failed A 2 Passed l 100v. Passed 30.000cycles 156W A4 I560 A 5 Failed Failed A-6 Passed Passed A9 150W A 1 0Failed Failed (900v.)

(control) EXAMPLE VH1 2. a balance of 0% up to about a catalytic amountA test belt identified as A-l l is prepared as in Exam- While the aboveExamples are directed to preferred embodiments of the invention, it willbe understood that the invention is not limited thereby.

of at least one of palladium chloride or chloroplatinic acid based onthe presence of a total amount of catalyst in effecting step (a), and

3. from 0% up through about 10% by weight of a water soluble alkalimetal halide or metal sulfate; about 8% 10% of the metal sulfate beingutilized in the absence of platinum or.palladium catalyst;

b. anodizing the washed microetched and oxidecoated substrate byimmersing and treating as an anode in an electrolytic bath until thepotential of the electrode as measured against a saturated calomelelectrode changes from a negative value not exceeding about 0.85 volt;and

S. A photoreceptor element of'claim 2 wherein the microetching step iseffected with an etching bath comprising phosphoric acid andchloroplatinic acid.

6. A photoreceptor element of claim 1 wherein the microetching step iseffected with an etching bath comprising phosphoric acidand palladiumchloride.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3, 914, 126

DATED October 21 1975 age 1 of 2 |NV ENTOR(S) Heinz W. Pinsler It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

[SEAL] Column 2 line 34, "satifactory" Column 5, line 20, "Afte" shouldbe After--.

Column 6, line 53, "3% of" omit the "of" Column 7, at the end of TableII, "g.=Good" should be G 0 0 Column 7, line 64, "conccentrated" shouldbe --concentrated-.

Column 8, line 28, insert rotatedbetween "constantly and "at".

Column 9, line 63, "40 seconds" Columns 5 and las shown on the attachedsheet should be added but will apply to the Grant only.

Sixth Day of July 1976 A ttes t:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner uj'PaIentsand Trademarks should be --40 minutes.

it is possible to prevent or at least to limit charge injection throughthe careful choice of interface materials having a work function suchthat they form a blocking layer with the photoconductive layer. ln thiscontext the term work function" is defined as a difference in energylevel between electrons present in a particular material and thosecalculated at infinite distance in vacuo; i.e., a binding energy. Withinthe above definition. an electron blocking contact is formed forxerographic purposes whenever the electronic work function of the metalsubstrate is larger than that of the overlying photoconductive insulatorlayer. if, on the other hand, the electronic work function of thesubstrate is smaller than the photoconductivc insulator, electrons areinjected into the system.

in attempting to determine the efficiency of a particular interface fromthe relative work functions of the joining materials, it has been foundthat small amounts .of adsorbed impurities on surfaces forming interfacematerials will also cause substantial changes in work function.Unfortunately, this can happen when amorphous selenium or seleniumalloys are utilized in a photoconductive layer. In fact, such materialcustomarily includes small amounts of chlorine and arsenic (ref.Xerography and Related Processes"; J. H. Dessauer and H. E. Clark). Theinjection ofelectrons from an interface area will dark-discharge aphotoreceptor when the photoconductor surface is charged positively anda negative electric counter charge is induced at the substrate.

it is further noted that a material which conducts only holes can alsobe employed as an electron blocking interface, provided it is depositedas a thin layer between the photoconductive layer and the chargeconducting substrate. Such material includes, for instance, chlorineandarsenic-rich selenium.

It is an object of the present invention to obtain improved flexiblephotoreceptor elements for xerographic copying purposes, in which anickel or nickelcoated charge conductive substrate layer and aphotoconductive layer, particularly a selenium-containingphotoconductive layer are strongly bonded without loss ofcharge-injection-blocking properties.

it is a further object of the present invention to obtainphotoconductive layers affixed to a nickel or nickelcoated substrate bychemically stable flex-proof bonding which is easily applied.

it is a still further object of the present invention to obtain, prepareand employ an efficient metal oxide blocking contact suitable for usewith a nickel-selenium alloy interface of a flexible belt-typephotoreceptor component.

These and other objects of the instant invention are accomplished bymicroetching a nickel or nickelcoated substrate such as nietallizedpaper or metallized plastic belt with an etching composition comprisingan inorganic acid, inclusive of phosphoric, sulfuric or hydrochloricacid, or combination thereof, in the pres ence of at least one ofpalladium chloride, chloroplatinic acid or ferric sulfate. This step isfollowed by anodizing the resulting microetched chemically oxidizedsubstrate, preferably by immersing the substrate as an anode in anelectrolytic bath and/or by glow discharge such as described. forinstance, by lgnatov in J. Chimie Physique, 54 (i957) pg. 96 et seq.

Page 2 of 2 When prepared by the first method it is found advantageousto immerse the substrate as an anode in an electrolyte bath until itspotential, as measured against a saturated calomel electrode, has amaximum value of about 0.85 volt. v

The substrate is then further treated by depositing a suitablephotoconductive layer. particularly a seleniuni-containingphotoconductive layer of one of the usual type upon the treatedsubstrate to obtain the desired photoreceptor element.

Preferably, nickel or nickel-covered substrate suitable for use inphotoreceptor elements within the present invention are kept free ofsurface contaminants, other than necessary additives such as dopants.This pre-condition can be easily obtained through the use of one or morecleaning steps wherein the substrate is initially immersed for a briefperiod into a cleaning bath. Suitable cleaners for such purpose are soldcommercially, and are exemplified. for instance, by Mitchell BradfordNo. 14 Cleaner" and by Mobil Acid Cleaner. The cleaned and well-rinsedsubstrate is optionally further treated with a pre -etch acid washsolution, preferably one containing an inorganic acid solution such ashydrochloric acid or phosphoric acid, and additionally containing 0% upto about a catalytic amount of at least one of palladium chloride orchloroplatinic acid. For such purpose a catalytic amount" is usefullydefined as the concentration of palladium chloride or chloroplatinicacid sufficient to substantially accellerate a combined etching andchemical oxidation reaction at the surface of the nickel substrate whenthe washed substrate is subsequently exposed to the required etching andoxidizing composition. Generally speaking, a satisfactory concentrationof catalyst in a pre-etch acid wash solution (when used) varies fromabout 0.01% 0.l0% by weight of solution, and the corresponding acidconcentration can usefully, although not exclusively, vary from about15% to 55% by weight.

When desired, the full catalytic amount of platinum or palladium can besupplied by inclusion of one or both in (a) the pre-etch acid washsolution, (b) in the etching composition, or (c) in both the washsolution and etching composition. in each case, however, a totalsolution concentration of about 0.01% 0.10% by weight is foundsufficient to assure an adequate cata' lytic deposition on the nickelbelt surface, provided proper temperature and time conditions are met.By way of example, a pre-etch acid washing step is prefe rably carriedout at a temperature range of about 15C C. for a period of about 1-5minutes.

The microetching step, on the other hand, can be usefully carried out ata somewhat higher temperature range of about 20C l 10C and for a periodof about 2-l5 minutes. Where increased concentration and/or differencesin temperature are permitted, however, the treatment time can be variedsomewhat without substantially affecting the desired properties.

Generally speaking, a suitable etching solution for purposes of thepresent invention can comprise i. an inorganic acid solution containingat least one of phosphoric acid, sulfuric acid or hydrochloric acid;

2. a balance of 0% up to about a catalytic amount of at least one ofpalladium chloride or chloroplatinic acid based on the total amount ofcatalyst utilized in the .acid wash and micro etching steps, and

1. A PHOTORECEPTOR ELEMENT COMPRISING A NICKEL OR NICKELCOATED SUBSTRATE AND A PHOTOCONDUCTIVE LAYER JOINTED IN GOOD BLOCKING AND CHARGE-INJECTION PREVENTING CONTACT WITH THE SUBSTRATE THROUGH AT LEAST TWO INTERMEDIATE NICKEL OXIDE BLOCKING LAYERS ARRANGED BETWEEN THE SUBSTRATE AND THE PHOTOCONDUCTIVE LAYER, OBTAINED BY THE PROCESS COMPRISING MICROETCHING TE NICKEL OR NICKEL-COATED SUBSTRATE WITH AN ETCHING COMPOSITION COMPRISING AN INOGANIC ACID SELECTED FROM THE GROUP CONSISTNG OF PHOSPHORIC ACID, SULFURIC ACID AND HYDROCHLORIC ACID, IN THE PRESENCE OF AT LEAST ONE OF PALLADIUM CHLORIDE, CHLOROPLATINIC ACID, OR FERRIC SULFATE, ANODIZING TE RESULTING MICROETCHED CHEMICALLY OXIDIZED SUBSTRATE, AND DEPOSITING A PHOTOCONDUCTIVE LAYER UPON THE TREATED SUBSTRATE TO OBTAIN THE DESIRED PHOTORECEPTOR ELEMENT.
 2. The photoreceptor element of claim 1 wherein the photoconductive layer is a selenium-containing photoconductive layer.
 2. a balance of 0% up to about a catalytic amount of at least one of palladium chloride or chloroplatinic acid based on the presence of a total amount of catalyst in effecting step (a), and
 3. from 0% up through about 10% by weight of a water soluble alkali metal halide or metal sulfate; about 8% - 10% of the metal sulfate being utilized in the absence of platinum or palladium catalyst; b. anodizing the washed microetched and oxide-coated substrate by immersing and treating as an anode in an electrolytic bath until the potential of the electrode as measured against a saturated calomel electrode changes from a negative value not exceeding about 0.85 volt; and c. depositing a selenium-containing photoconductive layer upon a surface of the treated and washed substrate to obtain the desired element.
 3. A photoreceptor element comprising a nickel or nickel-covered substrate and a selenium-containing photoconductive layer joined in good blocking contact through at least two intermediate blocking layers arranged between said substrate and the applied photoconductive layer, obtained by the process a. microetching the nickel or nickel-coated substrate with an etching composition comprising
 4. The photoreceptor of claim 3 wherein clean nickel or nickel-coated substrate is treated with a pre-etch acid solution additionally containing 0% up to about a catalytic amount of at least one of palladium chloride or chloroplatinic acid prior to the microetching step.
 5. A photoreceptor element of claim 2 wherein the microetching step is effected with an etching bath comprising phosphoric acid and chloroplatinic acid.
 6. A photoreceptor element of claim 1 wherein the microetching step is effected with an etching bath comprising phosphoric acid and palladium chloride. 